1. Field of the Invention
The present invention relates to a blasting material to be used in a blasting process carried out for removing a paint and so on from a surface of a target metal before forming a sprayed coating thereon for the purpose of preventing the target metal from being rusted. The present invention further relates to a blasting process in which the above-mentioned blasting material is used.
2. Description of the Related Art
As one of blasting processes in which abrasives such as sand are sprayed by compressed air onto a paint coating for removing the paint coating, there is generally used a dry-type blasting process in which abrasives in dry condition are employed. In a dry-type blasting process, dust is generated because abrasives come into collision with a target and the target is crushed, and further, dust is also generated of removed paint coating and metal oxide such as rust having been generated on a surface of steel on which the paint coating was coated. In particular, when a building in a town and/or a bridge over a river are to be repainted, much costs are necessary for a countermeasure to such dust.
Consequently, many attempts have been made in a dry-type blasting process for preventing dust from generating and dispersing. In a dry-type blasting process, since dust is broadly dispersed, it is difficult to carry out the blasting process in open space. Thus, for instance, Japanese Patent No. 2880498 has suggested a blasting apparatus which is designed to have a function of spraying water, if necessary, at a spray nozzle through which abrasives are sprayed, and hence, is capable of carrying out a wet-type blasting process.
The article “Wet-particle blasting” (retrieved on Nov. 22, 2010 at the site of SNM Asia Corporation (URL: http://snmasia.jp/blaster/blaster01.html)) has suggested wet-particle blasting in which abrasives filled in a tank are compressed by hydraulic pressure, the abrasives are dispensed by a predetermined amount with water existing only between the abrasives, and the abrasives are sprayed together with blast air. In the suggested wet-particle blasting, at a moment when the wet abrasives come into collision with a target, hydraulic films are released like a parachute to thereby prevent generation of dust.
In a process like the above-mentioned Japanese Patent where water films are formed when dry abrasives are sprayed onto a target to thereby prevent generation of dust, it is necessary to spray much water for reducing an amount of dust, because water captures dust for preventing dust from dispersing. In addition, since much waste water is generated, a water treatment equipment is inevitably necessary for cleaning such waste water.
The blasting apparatus suggested in the above-mentioned Japanese Patent is designed to include a tank in which dry abrasives are stored, a main body having a dispenser for dispensing the abrasives in a predetermined amount, a tank storing therein water to be sprayed, a water pump for pressurizing and feeding water, a nozzle through which the abrasives are sprayed together with water, and hoses for connecting the tanks, the water pump, and the nozzle to one another. The blasting apparatus is inevitably large-sized.
Furthermore, through water is mixed into the nozzle in the suggested blasting apparatus, water may be mixed to the abrasives while the abrasives and air are fed together in such a condition that they are mixed with each other. However, a volume of air is remarkably greater than a volume of water and the abrasives in the suggested blasting apparatus. Thus, in actual, air, water and the abrasives are merely mixed in separate condition, and accordingly, each particle of the abrasives cannot be sufficiently wet.
In addition, in the blasting apparatus suggested in the above-mentioned Japanese Patent, since it is difficult to set the large-sized apparatus at its entirety on a scaffold when the apparatus is used in an actual construction site, the apparatus has to be set on the ground in the vicinity of a target to which a blasting process is to be carried out. Thus, a hose through which a spray nozzle and a tank is connected to each other is inevitably lengthy, resulting in deterioration in the performance and an air compressor for supplying compressed air, which makes the blasting apparatus to be larger in size.
In the process suggested in the above-identified article “Wet-particle blasting”, the abrasives are merely made wet by forcing out the abrasives by means of hydraulic pressure. Thus, it is not possible to control a volume of water, and a volume of water is not uniform, and hence, an excessive volume of water actually tends to be sprayed.
In particular, when a blasting newly starts, there is a problem that a blasting cannot be started until pressurized water sufficiently penetrates spaces formed between the abrasives.